This application relates to advanced control systems for HVAC systems that integrate testing of forced air duct leakage and building envelope infiltration, the monitoring of energy efficiency in the conditioning of buildings, the prediction of financial costs or savings from thermostat setting changes, and the monitoring of ongoing operating parameters and space conditioning costs.
Envelope infiltration and duct leakage are recognized as two of the largest wastes of energy in U.S. homes and other buildings. Infiltration in older homes is typically several times what is needed for healthy ventilation. The average California forced air duct system leaks 30%. Reducing these expensive and carbon-generating forms of leakage is universally recognized as being among the most cost effective energy retrofit measures in existing buildings and a requirement for new construction also. Testing duct leakage and infiltration against standards is becoming universal in an era of global climate change and rising energy costs, but currently require expensive equipment and a trained technician.
The 2012 versions of the International Residential Code, adopted in 49 states and the International Energy Conservation Code, adopted in 46 states, as state-wide building codes, require that both infiltration and duct leakage be measured and verified to be within strict limits, in new construction. The same standards have been widely adopted globally. Under the 2013 California Title 24 standards, duct leakage must be tested and proven less than 6% of nominal airflow and infiltration must be tested and verified to be under a limit. Other standards, such as ASHRAE Standard 152, and ASTM Standard Test Method for Determining Air Leakage Rate by Fan Pressurization, ASTM E 779, specify how leakage should be tested in new and existing buildings. The present system addresses the unrecognized problem of reducing the costs of this mandated testing.
Studies of duct sealing retrofits have shown reductions in heating costs of 16-18% at relatively low cost. However, programs to retrofit existing buildings have reached only a small fraction of the base of residential construction. In 2009, the US Census Bureau reported housing units totaling 130,159,000 of which very few have been tested, much less retrofitted. The large federal weatherization assistance program (WAP), which provides energy retrofits completely free to low income homeowners, has reached only 6.4 million low-income households during the past 33 years. New approaches are needed to assure building energy efficiency in many more existing buildings
The measurement of both forms of leakage currently requires test equipment costing thousands of dollars, and hours of a specially trained and certified technician, who typically makes a special visit just to conduct the tests. Most HVAC installation companies in the U.S. do not even own the necessary test equipment, and the job is left to HERS raters in new buildings and energy auditors for existing buildings. When buildings fail the tests as they often do, repeat testing is required. The most effective method of fixing leaks includes using the test equipment to continuously monitor sealing progress and to conduct “post” tests, involving hours more of skilled labor often needed at times when the test equipment and technician may not be available. Scheduling the equipment and technician can result in expensive project delays. The unrecognized problem solved by the present system, is that the expertise to audit and improve the efficiency of houses and other small buildings needs to be simplified, made more accessible and shared more widely. Also, the system permits personnel installing HVAC to pre-test for leakages to insure that an official test by a certified person will be passed.
It has been well documented for many years that even well-designed buildings have significant inefficiencies due to lack of regular testing, maintenance and repairs. Contributing to this problem is the lack of low cost monitoring and alerting technology. Gross problems leading to poor efficiency can persist for many years undetected. The present system is a solution to this long unsolved problem by monitoring of HVAC operating parameters and overall heating and cooling efficiencies, issuing specific alerts when equipment or the building space itself needs attention.
Studies have shown that proper use of nighttime setbacks in programmable thermostats is capable of saving up to 15% of heating and cooling costs. However, many other studies that indicate the few thermostats are property programmed to achieve such savings. The present system encourages the use of setbacks by improving the user interface, predicting the financial savings that are possible for specific setbacks, using cost information derived by logging past building energy use and costs and volunteering suggestions for energy savings.
The three novel sets of features: for leakage testing, maintenance alerts, and energy cost prediction are combined into a single integrated system—a programmable thermostat with advanced energy saving features with improvements to the air handler it controls. A wide range of embodiments can implement some or all of the novel features.